Tensioners for flexible drive systems, and in particular for flexible drive systems comprising accessory drive systems on internal combustion engines, are well known. Such tensioners include a pulley which is biased toward the flexible drive, typically a rubber belt. The pulley is mounted to a pivot arm which is biased towards the flexible drive (the tensioning direction) by a spring and the pivot arm can also include means to produce a dampening force to inhibit oscillation of the pivot arm and/or flexible drive. Prior art tensioners which provide frictional dampening typically provide a frictional force using a damping mechanism made of materials such as plastic or metallic.
Bushings used on the prior art tensioner pivot arms may use PTFE to facilitate movement.
Representative of the art is U.S. Pat. No. 8,142,314 which discloses a tensioner which employs a spindle and a tensioner arm which are preferably manufactured by a suitable manufacturing process, such as die casting, negating a requirement for machining operations. The biasing spring of the tensioner is wound with wire having a non-circular cross section to increase the spring force of the spring compared to a similar spring wound with wire of circular cross section and, as the tensioner arm is moved away from the flexible drive, the diameter of the biasing spring expands and the coils press a dampening shoe into contact with a wall of the tensioner arm producing a dampening force. The tensioner is simple to assemble and requires a relatively small package volume for the biasing force it can produce.
What is needed is a tensioner having a damping shoe comprising PTFE mixed within a plastic matrix material, the PTFE comprising between approximately 2% and 4% of the plastic matrix material by weight. The present invention meets this need.